devextreme/dist/transpiled/core/utils/queue.js

HTML5 JavaScript Component Suite for Responsive Web Development

"use strict";

var errors = require("../errors"),
    when = require("../../core/utils/deferred").when;

function createQueue(discardPendingTasks) {
    var _tasks = [],
        _busy = false;

    function exec() {
        while (_tasks.length) {
            _busy = true;

            var task = _tasks.shift(),
                result = task();

            if (result === undefined) {
                continue;
            }

            if (result.then) {
                // NOTE: immediate "then" on the next line can reset it back to false
                when(result).always(exec);
                return;
            }

            throw errors.Error("E0015");
        }

        _busy = false;
    }

    function add(task, removeTaskCallback) {
        if (!discardPendingTasks) {
            _tasks.push(task);
        } else {
            if (_tasks[0] && removeTaskCallback) {
                removeTaskCallback(_tasks[0]);
            }
            _tasks = [task];
        }
        if (!_busy) {
            exec();
        }
    }

    function busy() {
        return _busy;
    }

    return {
        add: add,
        busy: busy
    };
}

exports.create = createQueue;
exports.enqueue = createQueue().add; // Default global queue for UI sync, consider renaming